Designing polyimide/polyacrylonitrile/polyimide sandwich composite separator for rechargeable lithium-ion batteries

The thermal stability of lithium-ion battery separator is very desirable to satisfy the requirements of EVs. Polyacrylonitrile (PAN) fiber membranes with excellent ionic conductivity and polyimide (PI) with excellent mechanical properties and flame retardancy have been attracted much attention. In this study, a PI/PAN/PI sandwich separator with three-dimensional network and sponge-like structures is prepared via electrostatic spinning, non-solvent phase separation and pressed lamination method. Compared with the cells with the typical PP separators, original PAN and PI separators, the cells assembled with the PI/PAN/PI sandwich separators presented an optimum rating and cycling capability, higher discharge capacity and lower internal resistance. The maximum discharge capacity of PI/PAN/PI separator was obtained 151.56 mAh g−1 at 0.1C, and the capacity retention could be maintained 94.3 % at 1C after 100 cycles during the charge and discharge process. Besides, the PI/PAN/PI separator exhibits excellent mechanical properties (18.12 MPa) and flame retardant performance. These results indicate that this process of PI/PAN/PI sandwich separator can be an efficient and applicable approach for preparing high performance separators, which will lead to stable cyclability and superior C-rate capacity.